1. Field of the Invention
This invention relates to tire-monitoring systems. More particularly it relates to the use of measurements made on tires to give one or more alarms.
2. Description of the Related Art
U.S. Pat. No. 4,703,650 describes a coding device that can be used for transmission of the pressure and temperature of a tire from the wheel to the vehicle. When a temperature of a tire on a vehicle is being continuously monitored, it is difficult to measure the exact temperature of the inflation air within the tire. It is important to exactly monitor this temperature since a pressure correction is made as a function of temperature. Precise temperature detection is also important if the ratio of the absolute temperature is to be divided by the absolute pressure, because it is this ratio which is proportional as a first approximation of a number of moles of gas in the tire, which should remain constant barring a leak of inflation fluid from the tire.
The temperature sensor is influenced by the temperature of the rim on which the tire is mounted. In almost all vehicles, this rim surrounds braking elements which dissipate a considerable amount of heat in use. This results in the detected temperature erroneously being higher than the actual temperature of the inside air during braking maneuvers. At other times the rim is usually at a temperature less than the inside temperature of the tire, resulting in an error by shortfall.
Other influences also disturb the estimation of the amount of air (number of moles) in the tires. Thus, during turning, the tires at the outside of the turn are flattened, causing a reduction in volume and so an increase in pressure, while the opposite occurs for the tires on the opposite side. Here again, errors by excess or shortfall can occur in the number of moles calculated.